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    <title>Document</title>
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    <script>
        var str = prompt("请输入一个字符串");

				function isNumber(str){
				if( str == 0){
				return true;
				}
				if( str == ""){
				}
				return !!Number(str); 
				}
				var res = isNumber(str);
				if(res == 0){
					alert("不是数字")
				}else{
					alert("是数字")
				}

    </script>
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